Interpretive Summary: Citrus huanglongbing (HLB)is a disease of citrus that has caused millions of dollars in losses to the US citrus industry. There are three species of the bacterium “Candidatus Liberibacter” associated with the disease. Among them, “Ca L. asiaticus” (Las) is the most prevalent and has been associated with the increasing economic losses to citrus production worldwide. In this report, a summary is provided for the research progress in Liberibacter genome sequencing, virulence gene identification and molecular profiles analysis of citrus hosts in response to HLB. As the bacterium has not been cultured, information regarding the general biology, physiology and pathogenicity of Las is limited. Since the publication of the Las genome, annotation of the Las genome has provided insights into the genetic basis of the virulence, physiological and metabolic capabilities of this organism. Since all commercial citrus cultivars are susceptible to HLB and current strategies of HLB control focus primarily on insect control, more research is needed to better understand the vector biology, disease mechanisms, host response and epidemiology of HLB in the context of vector-pathogen-plant interactions. These research efforts will facilitate the development of sustainable, effective and integrated management strategies for HLB.

Technical Abstract:
The purpose of this talk is to provide research progress for genomic and proteomic study of pathogen-host interactions of citrus huanglongbing (HLB), a destructive disease of citrus that represents a major threat to the citrus industries in US as well as other citrus production regions in the world. The disease is associated with a gram-negative, phloem-limited, insect-vectored, unculturable prokaryote: “Candidatus Liberibacter spp” that belongs to the Rhizobiaceae family of Alpha-Proteobacteria. In spite of the fact that Koch’s postulates have not been fulfilled, a great amount of research progress has been made in understanding molecular basis of HLB disease since the publication of the HLB-associated Liberibacter genome. Annotation of the Liberibacter genome sequence has provided insights into the genetic basis of virulence, physiological and metabolic capabilities of this organism. Functional determination of key virulence genes will permit researchers to design and develop novel gene-based therapeutic treatments to control the disease. Unfortunately, all commercial citrus cultivars are susceptible to HLB. Thus, understanding molecular mechanisms of host response will advance knowledge of the genetic basis of HLB. A long term and sustainable management of HLB requires integrated strategies including removal or reduction of vectors or inocula, and the improvement of host resistance to HLB-associated Liberibacters and psyllid vectors.